Serial axial flow fan

ABSTRACT

A serial axial flow fan in which an end portion of a first axial flow fan on an exhaust side, and an end portion of a second axial flow fan on an intake side are connected to each other. At least either of a plurality of first blades of a first impeller of the first axial flow fan, and a plurality of second blades of a second impeller of the second axial flow fan are provided with auxiliary blade portions. Furthermore, Nin&lt;Nout&lt;Nrib is satisfied, where a number of first blades is Nin, a number of second blades is Nout, and a number of first support ribs and a number of second support ribs are each Nrib.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. PatentApplication No. 62/445,355 filed on Jan. 12, 2017 and Japanese PatentApplication No. 2018-001030 filed on Jan. 9, 2018. The entire contentsof these applications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a serial axial flow fan in which axialflow fans are directly connected to each other.

2. Description of the Related Art

Hitherto, axial flow fans are used as cooling fans that cool electroniccomponents disposed inside casings. Static pressure and air volumerequired in a cooling fan are on the rise due to an increase in heatgenerating amounts of electronic components caused by increase inperformance, and due to an increase in the density where the electroniccomponents are disposed caused by miniaturization of the casing. Inorder to increase the static pressure and the air volume of the coolingfan, serially disposed axial flow fans, such as the one described inJapanese Laid-open Patent Application Publication No. 2007-303432 inwhich two (a plurality of) axial flow fans are serially connected toeach other in an axial direction, are proposed.

Furthermore, a counter-rotating axial flow fan of patent literature 2includes a first impeller on a suction side, a second impeller on adischarge side, and a stator blades disposed in a static state at aposition between the first impeller and the second impeller.Furthermore, it is disclosed that the air volume and the static pressureare the highest when the number of blades of the first impeller is five,the number of stator blades is three, and the number of second impellersis four.

In recent years, the amount of heat generated by electronic componentsis increasing, and the density in which the electronic components aredisposed inside a casing is getting higher. Furthermore, there are casesin which the air from the serially disposed axial flow fan does noteasily spread inside the casing due to a formation of a portion wherethe gap between the components are small, and due to another electroniccomponent being disposed behind an electronic component. The electroniccomponents may become insufficiently cooled due to hindrance in thespreading of the airflow.

SUMMARY OF THE INVENTION

An object of the present disclosure is to provide a serial axial flowfan that is capable of improving the static pressure and the air volumewith regards to the input shaft power, and that is capable of reducingnoise.

An exemplification of a serial axial flow fan according to the presentdisclosure includes a first axial flow fan that blows out air drawn infrom an intake side to an exhaust side, a second axial flow fanconnected to the first axial flow fan along a central axis of the firstaxial flow fan, the second axial flow fan blowing out the air drawn infrom an intake side to an exhaust side, wherein an end portion of thefirst axial flow fan on the exhaust side and an end portion of thesecond axial flow fan on the intake side are connected to each other,the first axial flow fan including a first impeller that rotates aboutthe central axis, a first motor portion that rotates the first impeller,a first housing that includes a first cylindrical portion that surroundsan outside of the first impeller in a radial direction, and a firstsupport rib that extends inwards from an inner surface of the firstcylindrical portion and that supports the first motor portion, the firstimpeller including a plurality of first blades that extend outwards inthe radial direction and that are arranged in a circumferentialdirection, the second axial flow fan including a second impeller thatrotates about the central axis, a second motor portion that rotates thesecond impeller, a second housing that includes a second cylindricalportion that surrounds an outside of the second impeller in the radialdirection, and a second support rib that extends inwards from an innersurface of the second cylindrical portion and that supports the secondmotor portion, a number of the second support ribs being equal to anumber of the first support ribs, and the second impeller including aplurality of second blades that extend outwards in the radial directionand that are arranged in the circumferential direction, auxiliary bladeportions being included in at least either of the first blades and thesecond blades, and Nin<Nout<Nrib being satisfied, where a number offirst blades is Nin, a number of second blades is Nout, and a number offirst support ribs and a number of second support ribs are each Nrib.

The exemplification of the serial axial flow fan of the presentdisclosure is capable of improving static pressure and air volume withregards to the input shaft power, and is capable of reducing noise.

The above and other elements, features, steps, characteristics andadvantages of the present disclosure will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a serial axial flow fanaccording to the present disclosure.

FIG. 2 is a cross-sectional view of the serial axial flow fanillustrated in FIG. 1 cut along a plane including a central axis.

FIG. 3 is a perspective view of the first axial flow fan viewed fromabove.

FIG. 4 is a perspective view of the first axial flow fan viewed frombelow.

FIG. 5 is an exploded perspective view of the first axial flow fanillustrated in FIG. 3.

FIG. 6 is a cross-sectional view of the first axial flow fan illustratedin FIG. 3 cut along a plane including the central axis.

FIG. 7 is a perspective view of a second axial flow fan viewed fromabove.

FIG. 8 is a perspective view of the second axial flow fan viewed frombelow.

FIG. 9 is an exploded perspective view of the second axial flow fanillustrated in FIG. 7.

FIG. 10 is a cross-sectional view of the second axial flow fanillustrated in FIG. 7 cut along a plane including the central axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the drawings. Note that in thepresent specification, in a serial axial flow fan 1, a directionparallel to a central axis J1 of the serial axial flow fan 1 is referredto as an “axial direction”, a direction orthogonal to the central axisJ1 of the serial axial flow fan 1 is referred to as a “radialdirection”, and a direction extending along an arc about a center of thecentral axis J1 of the serial axial flow fan 1 is referred to as a“circumferential direction”. Furthermore, in the serial axial flow fan1, the axial direction is referred to as an up-down direction, and anupper side IS and a lower side OS are defined with the state illustratedin FIG. 1 as a reference. Note that the up-down direction is a term usedfor description and does not limit the positional relationship and thedirection of the serial axial flow fan 1 while in use.

A serial axial flow fan of an exemplary embodiment of the presentdisclosure will be described hereinafter. FIG. 1 is a perspective viewof an example of a serial axial flow fan according to the presentdisclosure. FIG. 2 is a cross-sectional view of the serial axial flowfan illustrated in FIG. 1 cut along a plane including the central axis.The serial axial flow fan 1 illustrated in FIGS. 1 and 2 draws in airthrough an end portion on the upper side IS. Furthermore, the air thathas been drawn in is compressed and (or) accelerated inside the serialaxial flow fan 1 and is discharged from an end portion on the lower sideOS. Note that in the description hereinafter, the upper side may bereferred to as an intake side, and the lower side may be referred to asan exhaust side.

As illustrated in FIGS. 1 and 2, the serial axial flow fan 1 includes afirst axial flow fan 2 and a second axial flow fan 3. The first axialflow fan 2 is disposed on the upper side of the second axial flow fan 3.In other words, the first axial flow fan 2 is disposed on the intakeside of the second axial flow fan 3. Furthermore, in the serial axialflow fan 1, the first axial flow fan 2 and the second axial flow fan 3are connected in series along the central axis J1. In other words,centers of the first axial flow fan 2 and the second axial flow fan 3coincides with the central axis J1.

The upper sides IS of the first axial flow fan 2 and the second axialflow fan 3 are both the intake sides, and the lower sides OS thereof arethe exhaust sides. Furthermore, the exhaust side of the first axial flowfan 2 and the intake side of the second axial flow fan 3 are connectedto each other. In other words, the air discharged through a firstexhaust portion 2302 described later provided at an end face of thefirst axial flow fan 2 on the lower side OS is drawn in through a secondintake portion 3301 described later provided at an end face of thesecond axial flow fan 3 on the upper side IS.

In other words, the first axial flow fan 2 blows the air drawn in fromthe intake side out from the exhaust side. Furthermore, the second axialflow fan 3 connected to the first axial flow fan 2 along the centralaxis J1 of the first axial flow fan 2 blows the air drawn in from theintake side out from the exhaust side. Furthermore, in the serial axialflow fan 1, the end portion of the first axial flow fan 2 on the exhaustside is connected to the end portion of the second axial flow fan 3 onthe intake side.

FIG. 3 is a perspective view of the first axial flow fan viewed fromabove. FIG. 4 is a perspective view of the first axial flow fan viewedfrom below. FIG. 5 is an exploded perspective view of the first axialflow fan illustrated in FIG. 3. FIG. 6 is a cross-sectional view of thefirst axial flow fan illustrated in FIG. 3 cut along a plane includingthe central axis. As illustrated in FIGS. 3 to 6, the first axial flowfan 2 includes a first impeller 21, a first motor portion 22, a firsthousing 23, and a plurality of first support ribs 24.

The first housing 23 is an outer package of the first axial flow fan 2,and protects the first impeller 21, the first motor portion 22, andother components.

The first housing 23 includes a first cylindrical portion 230, a firstintake flange portion 2311, and a first exhaust flange portion 2321. Thefirst cylindrical portion 230 is a cylinder penetrating from an upperend portion 231 to a lower end portion 232 along the central axis J1.The upper end portion 231 of the first cylindrical portion 230 is afirst intake portion 2301, and the lower end portion 232 is the firstexhaust portion 2302. As illustrated in FIGS. 3 to 6, the firstcylindrical portion 230 includes four outer flat surfaces 236 eachhaving a shape formed when the outer peripheral surface of the circularcylinder is cut by a plane parallel to the central axis J1. The outerflat surfaces 236 are disposed at equal intervals in the circumferentialdirection. The outer flat surfaces 236 are surfaces that are parallel tothe central axis J1.

In the first axial flow fan 2, the first impeller 21 rotates insidefirst cylindrical portion 230 about the central axis J1, and generatesan airflow. In other words, while the first cylindrical portion 230 is aportion of the outer package, the first cylindrical portion 230 is alsoa wind tunnel. In other words, the first housing 23 includes the firstcylindrical portion 230 that surrounds the other side of the firstimpeller 21 in the radial direction. Furthermore, the first impeller 21rotates about the central axis J1.

The first intake flange portion 2311 is provided at the upper endportion 231 of the first housing 23. The first intake flange portion2311 has a square shape when viewed in a central axis J1 direction and alength of each side is longer than an inside diameter of the firstcylindrical portion 230. Corner portions of the first intake flangeportion 2311 when viewed in the central axis J1 direction expand fromthe outer peripheral surface of the first cylindrical portion 230towards the outside in the radial direction. Note that the cornerportions are portions that include the corners of the square, and areportions that include the areas having a predetermined width in thecircumferential direction that include the corners. Corner portionsdescribed hereinafter will be similar to the above corner portions.Furthermore, the surfaces that constitute the sides of the square firstintake flange portion 2311 when viewed in the central axis J1 directionare each flush with the corresponding outer flat surface 236.

The first exhaust flange portion 2321 is provided at the lower endportion 232 of the first housing 23. The first exhaust flange portion2321 has a square shape when viewed in the central axis J1 direction anda length of each side is longer than the inside diameter of the firstcylindrical portion 230. Corner portions of the first exhaust flangeportion 2321 when viewed in the central axis J1 direction expand fromthe outer peripheral surface of the first cylindrical portion 230towards the outside in the radial direction. Furthermore, the surfacesthat constitute the sides of the first exhaust flange portion 2321 whenviewed in the central axis J1 direction are each flush with thecorresponding outer flat surface 236. Moreover, when viewed in thecentral axis J1 direction, the first intake flange portion 2311 and thefirst exhaust flange portion 2321 overlap each other.

The first cylindrical portion 230 includes a first inside diameterportion 233 and a second inside diameter portion 234. The first insidediameter portion 233 is disposed on the intake side with respect to thesecond inside diameter portion 234, in other words, the first insidediameter portion 233 is disposed on the upper side IS. The first insidediameter portion 233 is tubular, and an inside diameter D11 thereof doesnot change in the axial direction. The minimum inside diameter of thefirst cylindrical portion 230 is the inside diameter D11. In otherwords, the first inside diameter portion 233 is a minimum insidediameter portion. In the first cylindrical portion 230, the secondinside diameter portion 234 is disposed on the lower end portion 232side, in other words, the second inside diameter portion 234 is disposedat the end portion on the exhaust side. The second inside diameterportion 234 includes a portion that has a diameter that is larger thanthat of the first inside diameter portion 233. The portions of thesecond inside diameter portion 234 that overlap the outer flat surfaces236 in the radial direction are inner flat surfaces 2341, and portionsthat connect the inner flat surfaces 2341 to each other in thecircumferential direction are inner curved surfaces 2342. The section ofthe lowermost side of each inner curved surface 2342 of the secondinside diameter portion cut along a plane orthogonal to the central axishas an arc shape and an inside diameter thereof is an inside diameterD12. Furthermore, the inside diameter D11 of the first inside diameterportion 233 is smaller than the inside diameter D12 of each inner curvedsurface 2342 of the second inside diameter portion 234.

The inner curved surfaces 2342 include conical portions 235. Eachconical portion 235 is a portion of a conical inner surface and thediameter of each conical portion 235 widens towards the lower side, inother words, the exhaust side.

The first axial flow fan 2 includes 11 first support ribs 24. The 11first support ribs 24 extend from the second inside diameter portion 234towards the inner side in the radial direction, and are disposed atequal intervals in the circumferential direction. Inner sides of thefirst support ribs 24 in the radial direction are connected to a baseportion 2221 (described later) of the first motor portion 22. With theabove, the first motor portion 22 is supported by the first housing 23with the first support ribs 24. The first housing 23, the first supportribs 24, and the base portion 2221 are formed as a resin molded bodyformed in an integrated manner with resin. In the first axial flow fan2, the first support ribs 24 are disposed on the lower end side of thefirst housing 23. In other words, the first support ribs 24 extend froman inner circumferential surface of the first cylindrical portion 230towards the inner side, and support the first motor portion 22.

When viewed in the central axis J1 direction, the first support ribs 24are disposed inside the first cylindrical portion 230. Furthermore, eachfirst support ribs 24 traverses at least a portion of the airflowgenerated inside the first cylindrical portion 230 with the rotation ofthe first impeller 21. The airflow generated by the rotation of thefirst impeller 21 has a velocity component in the axial direction andhas a velocity component in the direction in which the first impeller 21rotates, in other words, in the circumferential direction. Accordingly,the first support ribs 24 each have an inclination that does not causethe airflow to flow back due to the velocity component of the airflow inthe circumferential direction, in other words, the first support ribs 24each have an inclination in which the lower side is positioned on thedownstream side in the rotation direction with respect to the upper sideIS. Although the details will be described later, when the first axialflow fan 2 and the second axial flow fan 3 are connected to each other,the first support ribs 24 and second support ribs 34 constitute statorblades, and regulates the airflow in the axial direction. In otherwords, the first support ribs 24 support the first motor portion 22 and,at the same time, serve as stator blades that regulate the airflow. Thefirst motor portion 22 is of a so-called outer rotor type. Asillustrated in FIG. 6, the first motor portion 22 includes a first rotorportion 221 and a first stator portion 222. The first motor portion 22rotates the first impeller 21.

The first stator portion 222 includes the base portion 2221, a bearingholding portion 2222, an armature 2223, and a circuit board 2224. Thebase portion 2221 is formed as an integrally molded body together withthe first housing 23 and the first support ribs 24. The base portion2221 has a disk shape orthogonal to the central axis J1. The center ofthe disk shape overlaps the central axis J1. The bearing holding portion2222 has a cylindrical shape, is disposed at a center portion of thebase portion 2221, and extends towards the upper side IS. Note that thebearing holding portion 2222 may be an integrally molded body moldedtogether with the base portion 2221. A ball bearing 2225 and a ballbearing 2226 are attached to an upper portion and a lower portion insidethe bearing holding portion 2222. Furthermore, a shaft 2213 (describedlater) of the first rotor portion 221 is rotatably supported through theball bearing 2225 and the ball bearing 2226. Note that the ball bearing2225 and the ball bearing 2226 are examples of a bearing mechanism, andthe bearing mechanism is not limited to the ball bearing 2225 and theball bearing 2226. Bearings that are structured to rotatably support theshaft 2213 may be widely employed.

The armature 2223 is fixed external to the bearing holding portion 2222in the radial direction. The armature 2223 includes a stator core 2227,a coil 2228, and an insulator 2229. The stator core 2227 is a stackedbody in which electromagnetic steel sheets are stacked in the axialdirection. Note that the stator core 2227 is not limited to a stackedbody in which electromagnetic steel sheets are stacked, and may be asingle member, such as a fired body of powder or a casting, for example.The stator core 2227 includes an annular core back and a plurality of(nine, herein) teeth. The nine teeth extend towards the outside in theradial direction from an outer peripheral surface of the core back andare formed radially. With the above, the nine teeth are arranged in thecircumferential direction. The coil 2228 is configured by winding alength of conducting wire around the teeth on which the insulator 2229has been attached.

The core back of the stator core 2227 is press-fitted in the bearingholding portion 2222, and the stator core 2227 is fixed to the bearingportion 2222. The press-fitting may be a so-called stationary fit, ormay be a light press-fit that is a so-called transition fit in which thepress-fitting force is weaker than the press-fitting. The core back andthe bearing holding portion 2222 may be fixed to each other by anothermethod, such as adhesion. When the stator core 2227 is fixed to thebearing holding portion 2222, the center thereof overlaps the centralaxis J1. Furthermore, the nine teeth of the stator core 2227 arearranged at equal intervals in the circumferential direction to smoothlyand efficiently rotate the first motor portion 22.

The circuit board 2224 is attached to the base portion 2221. The circuitboard 2224 is electrically connected to the coil 2228 of the firststator portion 222. The circuit board 2224 includes a drive circuit thatdrives the coil 2228.

The base portion 2221 of the first stator portion 222 is an integrallymolded body formed together with the first support ribs 24. With theabove, the first stator portion 222, in other words, the first motorportion 22 is supported by the first support ribs 24. Furthermore, thefirst support ribs 24 are also an integrally molded body formed togetherwith the first housing 23. Accordingly, the first motor portion 22 isconnected to the first housing 23 through the first support ribs 24, inother words, the first motor portion 22 is supported by the firsthousing 23.

The first rotor portion 221 includes a yoke 2211, a field magnet 2212,the shaft 2213, and a shaft fixing member 2214. The yoke 2211 is made ofmetal and has a lidded cylindrical shape about the central axis J1. Theshaft fixing member 2214 is fixed to the center of the lid-shapedportion of the yoke 2211. The shaft 2213 is fixed to the shaft fixingmember 2214 with a fixing method, such as press-fitting. Note that thefixing method is not limited to press-fitting and may be another method,such as adhesion. In other words, the yoke 2211 is fixed to the shaft2213 through the shaft fixing member 2214.

The field magnet 2212 has a circular cylinder shape. The field magnet2212 is fixed to an inner surface of the yoke 2211. The field magnet2212 is magnetized to the N-pole and the S-pole alternately in thecircumferential direction. Note that in place of the field magnet 2212having a circular cylinder shape, a plurality of field magnets may bearranged in the circumferential direction.

The shaft 2213 is made of metal and has a columnar shape. The shaft 2213is rotatably supported by the bearing holding portion 2222, in otherwords, by the first stator portion 222 through the ball bearing 2225 andthe ball bearing 2226. The center of the shaft 2213 rotatably supportedby the bearing holding portion 2222 overlaps the central axis J1.

In the first motor portion 22, by having the shaft 2213 be rotatablysupported through the ball bearing 2225 and the ball bearing 2226, thefirst rotor portion 221 is supported by the first stator portion 222 ina rotatable manner about the central axis J1. In the above, an innersurface of the field magnet 2212 of the first rotor portion 221 in theradial direction and an outer surface of the stator core 2227 in theradial direction oppose each other with a gap therebetween in the radialdirection. An operation of the first motor portion 22 will be describedin detail later.

As illustrated in FIGS. 5 and 6, the first impeller 21 includes aplurality of first blades 211, a cup 212, and auxiliary blade portions213. The cup 212 has a lidded cylindrical shape. Note that while the cup212 has a lidded cylindrical shape, the shape is not limited to theabove, and may be a truncated cone shape in which the outside diametersof an outer peripheral surface differ in the axial direction.

The first blades 211 each protrude from the outer surface of the cup 212in the radial direction towards the outside in the radial direction. Thefirst impeller 21 is provided with five first blades 211. The five firstblades 211 are aligned at equal intervals in the circumferentialdirection. In other words, the first impeller 21 includes the pluralityof first blades 211 that extend outwards in the radial direction andthat are arranged in the circumferential direction. The first blades 211are inclined in the circumferential direction and generate an airflowfrom the upper side towards the lower side when the first impeller 21 isrotated. In other words, the first blades 211 are each inclined to adirection that generates an airflow from the upper side IS towards thelower side. Surfaces of the first blades 211 on the exhaust side, inother words, the surfaces on the lower side are the pressure surfaces.Furthermore, surfaces of the first blades 211 on the intake side, inother words, the surfaces on the upper side IS are negative pressuresurfaces.

Furthermore, the auxiliary blade portions 213 are provided at outer edgeportions of the first blades 211 in the radial direction. With the aboveconfiguration, a vortex can be generated by the auxiliary blade portions213 and the backflow of air in the gaps between outer edge portions ofthe auxiliary blade portions 213 in the radial direction and an innersurface of the first cylindrical portion 230 can be suppressed. Detailswill be described later. The auxiliary blade portions 213 are eachformed in the entire area of the outer edge portion of the correspondingfirst blade 211 from a front end in the rotation direction to a rear endin the rotation direction. By configuring the auxiliary blade portions213 in the above manner, the pressure in the entire outer edge portionsof the first blades 211 can be increased with the auxiliary bladeportions 213. With the above, a pressure increasing effect can beobtained. Furthermore, there are cases in which the manufacturing iseasier compared with a case in which the auxiliary blade portion 213 isformed in a portion of the outer edge portion. Moreover, the auxiliaryblade portions 213 are each warped towards the outside in the radialdirection and to the upper side in the axial direction, in other words,to the intake side. With the above configuration, the pressure generatedwith each auxiliary blade portion can be increased with the auxiliaryblade portion with a simple shape. Furthermore, manufacturing is easiercompared to a configuration in which the auxiliary blade portions areattached in an additional manner.

In the first axial flow fan 2, an inflow of air in the outer edgeportions of the first blades 211 in the radial direction from thepressure surface side towards the negative pressure surface side issuppressed with the auxiliary blade portions 213. Note that an operationof suppressing the flow of air will be described in detail later.

As described above, the first stator portion 222 of the first motorportion 22 is assembled by attaching the bearing holding portion 2222,the armature 2223, and the circuit board 2224 to the base portion 2221formed integrally with the first housing 23. In other words, the firststator portion 222 is supported by the first housing 23 through thefirst support ribs 24.

Furthermore, the yoke 2211 of the first rotor portion 221 is fixedinside the cup 212 of the first impeller 21. The yoke 2211 may be fixedin the cup 212 by press-fitting or by adhesion. Furthermore, the yoke2211 may be fixed with a fastening member, such as a screw. The cup 212suppressing deviation from the yoke 2211 is fixed to the yoke 2211. Inother words, the first impeller 21 is fixed to the first rotor portion221.

Furthermore, the shaft 2213 of the first rotor portion 221 to which thefirst impeller 21 is fixed is fixed to the inner rings of the ballbearing 2225 and the ball bearing 2226 attached inside the bearingholding portion 2222. Note that while the shaft 2213 is fixed to theinner rings of the ball bearing 2225 and the ball bearing 2226 bypress-fitting, the fixing method is not limited to press-fitting. Forexample, a fixing method, such as adhesion or welding, that suppressesthe relative movement between the shaft 2213 and the inner rings, andthat fixes the shaft 2213 about the central axis J1 in a rotatablemanner can be widely employed. The first rotor portion 221 to which thefirst impeller 21 is attached is rotatably attached to the first statorportion 222 in the above manner.

By attaching the first rotor portion 221 to the first stator portion222, the first impeller 21 is accommodated inside the first housing 23.The outer sides of the auxiliary blade portions 213 in the radialdirection, the auxiliary blade portions 213 being provided at the outeredge portions of the first blades 211 in the radial direction, opposethe inner surface of the first cylindrical portion 230 in the radialdirection.

An electric current is supplied to the coil 2228 of the first motorportion 22 at a good timing from the drive circuit mounted on thecircuit board 2224. With the above, the first rotor portion 221 of thefirst motor portion 22 is rotated in a predetermined direction. Notethat, herein, the rotation direction of the first rotor portion 221 isanticlockwise when viewing the central axis J1 from the upper side IS.

By rotating the first motor portion 22 about the central axis J1, thefirst impeller 21 fixed to the first rotor portion 221 is also rotatedabout the central axis J1. With the rotation of the first impeller 21,an airflow that, while swirling in the circumferential direction, flowsin the axial direction is generated in the first housing 23, in otherwords, inside the first cylindrical portion 230.

With the rotation of the first impeller 21, the first blades 211 pushthe air. Accordingly, the surfaces on the lower side (the surfaces onthe exhaust side) of the first blades 211 are pressure surfaces, and thesurfaces on the upper side IS (the surfaces on the intake side) arenegative pressure surfaces. The first impeller 21 has five first blades211, and the inclination of each first blade 211 with respect to thecentral axis J1 is large. Accordingly, a pressure difference betweeneach pressure surface and the corresponding negative pressure surface islarge. In the first axial flow fan 2, the outer edge portions of thefirst blades 211 in the radial direction and the inner surface of thefirst cylindrical portion 230 oppose each other in the radial directionwith a gap in between. Accordingly, when the first impeller 21 isrotated and a pressure difference is generated in the first bladesbetween the pressure surfaces and the negative pressure surfaces, a flowof air from the pressure surface side towards the negative pressuresurface side, in other words, from the lower side OS towards the upperside IS, is easily generated in the outer edge portions of the firstblades 211 in the radial direction.

The auxiliary blade portions 213 are provided at the outer edge portionsof the first blades 211 in the radial direction. The auxiliary bladeportions 213 are warped towards the upper side IS (the intake side).When the first impeller 21 is rotated, the auxiliary blade portions 213generate a vortex in the gap between the outer edge portions of theauxiliary blade portions 213 in the radial direction and the innersurface of the first cylindrical portion 230. With the above vortex, aflow of air on the lower side towards the upper side in the gap betweenthe outer edge portions of the auxiliary blade portions 213 and theinner surface of the first cylindrical portion 230 can be suppressed.Accordingly, by suppressing the flow of air from the lower side towardsthe upper side, a decrease in the pressure difference between thepressure surfaces and the negative pressure surfaces is suppressed, inother words, pressure loss is suppressed. As a result, the first axialflow fan 2 is capable of discharging an airflow with high pressurethrough the first exhaust portion 2302. A vortex is formed in the gapbetween the inner surface of the first cylindrical portion 230 and theouter edge portions of the auxiliary blade portions 213 in the radialdirection, and backflow of air in the gap is suppressed by the vortex.In order to have the vortex effectively suppress the backflow of air inthe gap between the inner surface of the first cylindrical portion 230and the outer edge portions of the auxiliary blade portions 213 in theradial direction, the gap between the inner surface of the firstcylindrical portion 230 and the outer edge portions of the auxiliaryblade portions 213 in the radial direction is desirably as narrow aspossible. Furthermore, the gap between the inner surface of the firstcylindrical portion 230 and the outer edge portions of the auxiliaryblade portions 213 in the radial direction is desirably uniform. Notethat the gap between the inner surface of the first cylindrical portion230 and the outer side of the auxiliary blade portions 213 in the radialdirection being uniform not only includes a case in which the gap isuniform in an accurate manner, but also may include a case in which thegap has variations that do not affect the operation of the first axialflow fan 2. With such a configuration, the gap can be prevented frombecoming partially large. With the above, partial change in the gap issuppressed and the pressure balance is maintained; accordingly, thefirst impeller 21 can rotate smoothly, and vibration, noise, and thelike are suppressed. In other words, noise of the serial axial flow fan1 can be reduced.

By making the gap between the inner surface of the first cylindricalportion 230 and the outer edge portions of the auxiliary blade portions213 in the radial direction uniform, the variation in the effect ofsuppressing the backflow with the vortex is suppressed. With the above,the pressure balance in the circumferential direction of the firstimpeller 21 is not easily lost. As a result, the first impeller 21 canbe rotated smoothly, and vibration and (or) noise can be suppressed. Inother words, noise of the serial axial flow fan 1 can be reduced.

The auxiliary blade portions 213 are contained inside the length of thefirst cylindrical portion 230 in the axial direction. Since theauxiliary blade portions 213 reliably oppose the first cylindricalportion 230, the pressure increasing effect can be increased.Furthermore, by containing the auxiliary blade portions 213 inside thecircular cylinder, the shape of each auxiliary blade portion 213 formingthe gap with the inner surface of the first cylindrical portion 230 inthe radial direction at an equal distance can be simplified. The ease ofmanufacturing the first impeller 21 is facilitated more, accordingly.Furthermore, by having the surfaces opposing the auxiliary bladeportions 213 in the radial direction be a circular cylinder, the changesin the outside diameters of the auxiliary blade portions 213 becomessmall, and the changes in the pressure and the flow velocity can besuppressed. With the above, the effect of increasing the pressure of thedischarged airflow can be increased.

In the first axial flow fan 2, desirably, the outer edges of theauxiliary blade portions 213 in the radial direction oppose the innersurface of the first inside diameter portion 233 of the firstcylindrical portion 230 in the radial direction. In other words, in theinner surface of the first cylindrical portion 230, at least the portionthat opposes the auxiliary blade portions 213 in the radial directionis, desirably, a circular cylinder. Since the change in the insidediameter of the portion of the first cylindrical portion 230 thatopposes the auxiliary blade portions 213 is small, the pressure and theflow velocity do not easily change and the pressure can be increased.

Note that the auxiliary blade portions 213 may oppose the second insidediameter portion 234 in the radial direction. In such a case as well,the shapes of the outer edges of the auxiliary blade portions 213 areshapes in which the gap between the outer edges of the auxiliary bladeportions 213 in the radial direction and the inner surface of the secondinside diameter portion 234, and the gap between the outer edges of theauxiliary blade portions 213 in the radial direction and the innersurface of the first inside diameter portion 233 are the same. With theabove configuration, the above-described effect of suppressing vibrationand (or) noise can be obtained. In other words, noise of the serialaxial flow fan 1 can be reduced.

Note that in the first impeller 21, the auxiliary blade portions 213 areeach formed in the entire area of the outer edge portion of thecorresponding first blade 211 in the radial direction from a front endin the rotation direction to a rear end in the rotation direction. Withthe above, the pressure loss is reduced, and the pressure of the airflowdischarged through the first exhaust portion 2302 is increased.Meanwhile, there are cases in which the pressure of the airflowdischarged through the first exhaust portion 2302 is required to be onlyof a certain amount. In such a case, the auxiliary blade portions 213may be formed in a partial manner in the outer edge portions of thefirst blades 211 in the radial direction from the front end in therotation direction to the rear end in the rotation direction. With theabove configuration, the pressure of the airflow discharged from thefirst exhaust portion 2302 can be adjusted. Note that the portions inwhich the auxiliary blade portions 213 are formed are, desirably, formedat the same portions in the plurality of first blades 211. With such aconfiguration, the distribution of pressure in each first blade 211 withthe corresponding auxiliary blade portion 213 can be the same orsubstantially the same, and the pressure acting on the first impeller 21can be balanced. With the above, vibrate and (or) noise can besuppressed.

In other words, noise of the serial axial flow fan 1 can be reduced.

FIG. 7 is a perspective view of the second axial flow fan viewed fromabove. FIG. 8 is a perspective view of the second axial flow fan viewedfrom below. FIG. 9 is an exploded perspective view of the second axialflow fan illustrated in FIG. 7. FIG. 10 is a cross-sectional view of thesecond axial flow fan illustrated in FIG. 7 cut along a plane includingthe central axis. As illustrated in FIGS. 7 to 10, the second axial flowfan 3 includes a second impeller 31, a second motor portion 32, a secondhousing 33, and the plurality of second support ribs 34.

The second housing 33 is an outer package of the second axial flow fan 3and the serial axial flow fan 1, and protects the second impeller 31,the second motor portion 32, and other components.

The second housing 33 includes the second cylindrical portion 330, asecond intake flange portion 3311, and a second exhaust flange portion3321. The second cylindrical portion 330 is a cylinder penetrating froman upper end portion 331 to a lower end portion 332 along the centralaxis J1. The upper end portion 331 of the second cylindrical portion 330is a second intake portion 3301, and the lower end portion 332 is asecond exhaust portion 3302. As illustrated in FIGS. 7 to 9, the secondcylindrical portion 330 includes four outer flat surfaces 336 eachhaving a shape formed when the outer peripheral surface of the circularcylinder is cut by a plane parallel to the central axis J1. The outerflat surfaces 336 are disposed at equal intervals in the circumferentialdirection. The outer flat surfaces 336 are surfaces that are parallel tothe central axis J1.

In the second axial flow fan 3, the second impeller 31 rotates insidesecond cylindrical portion 330 about the central axis J1, and generatesan airflow. In other words, while the second cylindrical portion 330 isa portion of the outer package, the second cylindrical portion 330 isalso a wind tunnel. In other words, the second housing 33 includes thesecond cylindrical portion 330 that surrounds the other side of thesecond impeller 31 in the radial direction. Furthermore, the secondimpeller 31 rotates about the central axis J1.

The second intake flange portion 3311 is provided at the upper endportion 331 of the second housing 33. The second intake flange portion3311 has a square shape when viewed in a central axis J1 direction and alength of each side is longer than an inside diameter of the secondcylindrical portion 330. Corner portions of the second intake flangeportion 3311 when viewed in the central axis J1 direction expand fromthe outer peripheral surface of the second cylindrical portion 330towards the outside in the radial direction. Furthermore, the surfacesthat constitute the sides of the square second intake flange portion3311 when viewed in the central axis J1 direction are each flush withthe corresponding outer flat surface 336.

The second exhaust flange portion 3321 is provided at the lower endportion 332 of the second housing 33. The second exhaust flange portion3321 has a square shape when viewed in the central axis J1 direction anda length of each side is longer than the inside diameter of the secondcylindrical portion 330. Corner portions of the second exhaust flangeportion 3321 when viewed in the central axis J1 direction expand fromthe outer peripheral surface of the f second cylindrical portion 330towards the outside in the radial direction. Furthermore, the surfacesthat constitute the sides of the second exhaust flange portion 3321 whenviewed in the central axis J1 direction are each flush with thecorresponding outer flat surface 336. Moreover, when viewed in thecentral axis J1 direction, the second intake flange portion 3311 and thesecond exhaust flange portion 3321 overlap each other.

The second cylindrical portion 330 includes a first inside diameterportion 333 and a second inside diameter portion 334. The first insidediameter portion 333 is disposed on the exhaust side with respect to thesecond inside diameter portion 334, in other words, the first insidediameter portion 333 is disposed on the lower side OS. The first insidediameter portion 333 is tubular, and an inside diameter D21 thereof doesnot change in the axial direction. The minimum inside diameter of thesecond cylindrical portion 330 is the inside diameter D21. In otherwords, the first inside diameter portion 333 is a minimum insidediameter portion. In the second cylindrical portion 330, the secondinside diameter portion 334 is disposed on the upper end portion 331side, in other words, the second inside diameter portion 334 is disposedat the end portion on the intake side. The portions of the second insidediameter portion 334 that overlap the outer flat surfaces 336 in theradial direction are inner flat surfaces 3341, and portions that connectthe inner flat surfaces 3341 to each other in the circumferentialdirection are inner curved surfaces 3342. The inner curved surfaces 3342include conical portions 335. Each conical portion 335 is a portion of aconical inner surface and the diameter of each conical portion 335widens towards the upper side, in other words, the intake side.

The section of the uppermost side of each inner curved surface 3342 ofthe second inside diameter portion 334 cut along a plane orthogonal tothe central axis has an arc shape and an inside diameter thereof is aninside diameter D22. Furthermore, the inside diameter D21 of the firstinside diameter portion 333 is smaller than the inside diameter D22 ofeach inner curved surface 3342 of the second inside diameter portion334.

Furthermore, when the first axial flow fan 2 and the second axial flowfan 3 are connected to each other, the second inside diameter portion234 of the first cylindrical portion 230 and the second inside diameterportion 334 of the second cylindrical portion 330 are connected to eachother in the axial direction in a continuous manner. In so doing, inorder to connect the inner curved surfaces 2342 of the second insidediameter portion 234 of the first cylindrical portion 230 and the innercurved surfaces 3342 of the second inside diameter portion 334 of thesecond cylindrical portion 330 to each other in a smooth manner, theinside diameter D12 and the inside diameter D22 are the same.

Furthermore, in order to connect the inner flat surfaces 2341 of thesecond inside diameter portion 234 of the first cylindrical portion 230and the inner flat surfaces 3341 of the second inside diameter portion334 of the second cylindrical portion 330 to each other in a smoothmanner, the inside diameter D11 and the inside diameter D12 are thesame.

Furthermore, the lower end portion 332 of the second cylindrical portion330 in the axial direction includes diameter expanded portions 337, inwhich the lower portions thereof in the axial direction are curvedoutwardly in the radial direction, at areas that overlap the cornerportions of the second exhaust flange portion 3321 in the radialdirection, in other words, in areas that overlap the inner curvedsurfaces 3342 of the second inside diameter portion 334 in the axialdirection. The inside diameters of the diameter expanded portions 337becomes gently larger as the diameter expanded portions 337 extend inthe direction of the airflow. By shaping the diameter expanded portions337 in the above manner, the airflow discharged through the secondexhaust portion 3302 of the second cylindrical portion 330 does notbecome disrupted easily. When the diameter expanded portion 337 is cutalong a plane including the central axis J1, the shape of the section isa curved surface. In other words, the diameter expanded portions 337 hasa so-called bell-mouth shape.

In other words, the second housing 33 includes, at the end portion onthe exhaust side, the square second exhaust flange portion 3321 that hassides that are each larger than the inside diameter of the innercircumferential surface of the second cylindrical portion 330. Theportions of the end portion of the inner circumferential surface of thesecond cylindrical portion 330 on the exhaust side that overlap thecorner portions of the second exhaust flange portion 3321 in the radialdirection are curved outwards in the radial direction towards the edgeon the exhaust side. With the above, by forming the diameter expandedportions 337 in shapes that expand gradually, even when compared with acase in which the diameter expanded portions 337 are formed as a cone,the airflow is not easily disturbed and decrease in the pressure and inthe air volume can be suppressed.

The second axial flow fan 3 includes 11 second support ribs 34. The 11second support ribs 34 extend from the second inside diameter portion334 towards the inner side in the radial direction, and are disposed atequal intervals in the circumferential direction. Inner sides of thesecond support ribs 34 in the radial direction are connected to a baseportion 3221 (described later) of the second motor portion 32. With theabove, the second motor portion 32 is supported by the second housing 33with the second support ribs 34. The second housing 33, the secondsupport ribs 34, and the base portion 3221 are formed as a resin moldedbody formed in an integrated manner with resin. In the second axial flowfan 3, the second support ribs 34 are disposed on the upper end portion331 side of the second housing 33. In other words, the second supportribs 34 extend from an inner circumferential surface of the secondcylindrical portion 330 towards the inner side, and support the secondmotor portion 32.

When viewed in the central axis J1 direction, the second support ribs 34are disposed inside the second cylindrical portion 330. In combinationwith the first support ribs 24 of the first axial flow fan 2, the secondsupport ribs 34 are used as stator blades. Accordingly, the secondsupport ribs 34 are inclined in the same directions as the first supportribs 24 when the second axial flow fan 3 is connected to the lower sideOS of the first axial flow fan 2. In other words, the lower sides of thesecond support ribs 34 in the axial direction are positioned on thedownstream side in the rotation direction of the first impeller 21.

The second motor portion 32 is of a so-called outer rotor type. Asillustrated in FIG. 10, the second motor portion 32 includes a secondrotor portion 321 and a second stator portion 322. The second motorportion 32 rotates the second impeller 31. The second stator portion 322includes the base portion 3221, a bearing holding portion 3222, anarmature 3223, and a circuit board 3224. The base portion 3221 is formedas an integrally molded body together with the second housing 33 and thesecond support ribs 34. The base portion 3221 has a disk shapeorthogonal to the central axis J1. The center of the disk shape overlapsthe central axis J1. The bearing holding portion 3222 has a cylindricalshape, is disposed at a center portion of the base portion 3221, andextends towards the lower side in the axial direction. Note that thebearing holding portion 3222 may be an integrally molded body moldedtogether with the base portion 3221. A ball bearing 3225 and a ballbearing 3226 are attached to an upper portion and a lower portion insidethe bearing holding portion 3222. Furthermore, a shaft 3213 (describedlater) of the second rotor portion 321 is rotatably supported throughthe ball bearing 3225 and the ball bearing 3226. Note that the ballbearing 3225 and the ball bearing 3226 are examples of bearings, and thebearings are not limited to the ball bearing 3225 and the ball bearing3226. Bearing that are structured to rotatably support the shaft 3213may be widely employed.

The armature 3223 is fixed external to the bearing holding portion 3222in the radial direction. The armature 3223 includes a stator core 3227,a coil 3228, and an insulator 3229. The stator core 3227 is a stackedbody in which electromagnetic steel sheets are stacked in the axialdirection. Note that the stator core 3227 is not limited to a stackedbody in which electromagnetic steel sheets are stacked, and may be asingle member, such as a fired body of powder or a casting, for example.

The stator core 3227 includes an annular core back and a plurality of(nine, herein) teeth. The nine teeth extend towards the outside in theradial direction from an outer peripheral surface of the core back andare formed radially. With the above, the nine teeth are arranged in thecircumferential direction. The coil 3228 is configured by winding alength of conducting wire around the teeth on which the insulator 3229has been attached. The core back of the stator core 3227 is press-fittedin the bearing holding portion 3222, and the stator core 3227 is fixedto the bearing portion 3222. The press-fitting may be a so-calledstationary fit, or may be a light press-fit that is a so-calledtransition fit in which the press-fitting force is weaker than thepress-fitting. The core back and the bearing holding portion 3222 may befixed to each other by another method, such as adhesion. When the statorcore 3227 is fixed to the bearing holding portion 3222, the centerthereof overlaps the central axis J1. Furthermore, the nine teeth of thestator core 3227 are arranged at equal intervals in the circumferentialdirection to smoothly and efficiently rotate the second motor portion32.

The circuit board 3224 is attached to the base portion 3221. The circuitboard 3224 is electrically connected to the coil 3228 of the secondstator portion 322. The circuit board 3224 includes a drive circuit thatdrives the coil 3228.

The base portion 3221 of the second stator portion 322 is an integrallymolded body formed together with the second support ribs 34. With theabove, the second stator portion 322, in other words, the second motorportion 32 is supported by the second support ribs 34. Furthermore, thesecond support ribs 34 are also an integrally molded body formedtogether with the second housing 33. Accordingly, the second motorportion 32 is connected to the second housing 33 through the secondsupport ribs 34, in other words, the second motor portion 32 issupported by the second housing 33.

The second rotor portion 321 includes a yoke 3211, a field magnet 3212,the shaft 3213, and a shaft fixing member 3214. The yoke 3211 is made ofmetal and has a lidded cylindrical shape about the central axis J1. Theshaft fixing member 3214 is fixed to the center of the lid-shapedportion of the yoke 3211. The shaft 3213 is fixed to the shaft fixingmember 3214 with a fixing method, such as press-fitting. Note that thefixing method is not limited to press-fitting and may be another method,such as adhesion. The yoke 3211 is fixed to the shaft 3213 through theshaft fixing member 3214.

The field magnet 3212 has a circular cylinder shape. The field magnet3212 is fixed to an inner surface of the yoke 3211. The field magnet3212 is magnetized to the N-pole and the S-pole alternately in thecircumferential direction. Note that in place of the field magnet 3212having a circular cylinder shape, a plurality of field magnets may bearranged in the circumferential direction.

The shaft 3213 is made of metal and has a columnar shape. The shaft 3213is rotatably supported by the bearing holding portion 3222, in otherwords, by the f second stator portion 322 through the ball bearing 3225and the ball bearing 3226. The center of the shaft 3213 rotatablysupported by the bearing holding portion 3222 overlaps the central axisJ1.

In the second motor portion 32, by having the shaft 3213 be rotatablysupported through the ball bearing 3225 and the ball bearing 3226, thesecond rotor portion 321 is supported by the second stator portion 322in a rotatable manner about the central axis J1. In the above, an innersurface of the field magnet 3212 of the second rotor portion 321 in theradial direction and an outer surface of the stator core 3227 in theradial direction oppose each other with a gap therebetween in the radialdirection. An operation of the second motor portion 32 will be describedin detail later.

As illustrated in FIGS. 9 and 10, the second impeller 31 includes aplurality of second blades 311, and a cup 312. The cup 312 has a liddedcylindrical shape. Note that while the cup 312 has a lidded cylindricalshape, the shape is not limited to the above, and may be a truncatedcone shape in which the outside diameters of an outer peripheral surfacediffer in the axial direction.

The second blades 311 each protrude from the outer surface of the cup312 in the radial direction towards the outside in the radial direction.The second impeller 31 is provided with seven second blades 311. Theseven second blades 311 are aligned at equal intervals in thecircumferential direction. In other words, the second impeller 31includes the plurality of second blades 311 that extend outwards in theradial direction and that are arranged in the circumferential direction.The second blades 311 are inclined in the circumferential direction andgenerate an airflow from the upper side IS towards the lower side OSwhen the second impeller 31 is rotated. In other words, the secondblades 311 are each inclined to a direction that generates an airflowfrom the upper side IS towards the lower side OS.

As described above, the second stator portion 322 of the second motorportion 32 is assembled by attaching the bearing holding portion 3222,the armature 3223, and the circuit board 3224 to the base portion 3221formed integrally with the second housing 33. In other words, the secondstator portion 322 is supported by the second housing 33 through thesecond support ribs 34.

Furthermore, the yoke 3211 of the second rotor portion 321 is fixedinside the cup 312 of the second impeller 31. The yoke 3211 may be fixedin the cup 312 by press-fitting or by adhesion. Furthermore, the yoke2211 may be fixed with a fastening member, such as a screw. The cup 312suppressing deviation from the yoke 3211 is fixed to the yoke 3211. Inother words, the second impeller 31 is fixed to the second rotor portion321.

Furthermore, the shaft 3213 of the second rotor portion 321 to which thesecond impeller 31 is fixed is fixed to the inner rings of the ballbearing 3225 and the ball bearing 3226 attached inside the bearingholding portion 3222. Note that while the shaft 3213 is fixed to theinner rings of the ball bearing 3225 and the ball bearing 3226 bypress-fitting, the fixing method is not limited to press-fitting. Forexample, a fixing method, such as adhesion or welding, that suppressesthe relative movement between the shaft 3213 and the inner rings, andthat fixes the shaft 3213 about the central axis J1 in a rotatablemanner can be widely employed. The second rotor portion 321 to which thesecond impeller 31 is attached is rotatably attached to the secondstator portion 322 in the above manner.

By attaching the second rotor portion 321 to the second stator portion322, the second impeller 31 is accommodated inside the second housing33. The outer sides of the second blades 311 in the radial directionoppose the inner surface of the second cylindrical portion 330 in theradial direction. Furthermore, the second blades 311 are containedinside the length of the second cylindrical portion 330 in the axialdirection. Furthermore, the gap in the radial direction between theinner surface of the second cylindrical portion 330 and the outer sidesof the second blades 311 in the radial direction is uniform. Note thatthe gap between the inner surface of the second cylindrical portion 330and the outer sides of the second blades 311 in the radial directionbeing uniform not only includes a case in which the gap is uniform in anaccurate manner, but also includes a case in which the gap hasvariations that do not affect the operation of the second axial flow fan3.

An electric current is supplied to the coil 3228 of the second motorportion 32 at a good timing from the drive circuit mounted on thecircuit board 3224. With the above, the second rotor portion 321 of thesecond motor portion 32 is rotated in a predetermined direction. Notethat, herein, the rotation direction of the second rotor portion 321 isanticlockwise when viewing the central axis J1 from the upper side IS.

By rotating the second motor portion 32 about the central axis J1, thesecond impeller 31 fixed to the second rotor portion 321 is also rotatedabout the central axis J1. With the rotation of the second impeller 31,an airflow that, while swirling in the circumferential direction, flowsin the axial direction is generated in the second housing 33, in otherwords, inside the second cylindrical portion 330.

Compared with the first blades 211 of the first axial flow fan 2, theinclination of each second blade 311 of the second axial flow fan 3 withrespect to the shaft is small, and the pressure difference between eachpressure surface and the corresponding negative pressure surface issmall. Accordingly, suppression of pressure loss can be achieved withoutproviding any auxiliary blade portions in the outer edge portions of thesecond blades 311 in the radial direction. Furthermore, in an impellerin which each blade has a small inclination with respect to the shaft,rather than an effect of compressing air, an effect of increasing theflow velocity is obtained more easily by rotation of the impeller. Inother words, compared with the first axial flow fan 2, the ability ofincreasing the discharge flow rate is high in the second axial flow fan3. In other words, compared with the second axial flow fan 3, theability of increasing the discharge pressure is high in the first axialflow fan 2. In the serial axial flow fan 1, the above axial flow fanshaving different abilities are connected in series to increase thepressure and the flow rate. A detailed description of the serial axialflow fan 1 will be given next.

The serial axial flow fan 1 is formed by serially connecting the firstaxial flow fan 2 and the second axial flow fan 3 to each other in theaxial direction. The lower end portion of the first axial flow fan 2 andthe upper end portion of the second axial flow fan 3 are connected toeach other. The first exhaust flange portion 2321 of the first axialflow fan 2 and the second intake flange portion 3311 of the second axialflow fan 3 are in contact with and are fixed to each other in the axialdirection. Screwing can be cited as a method for fixing the firstexhaust flange portion 2321 and the second intake flange portion 3311 toeach other; however, the method is not limited to screwing. For example,adhesion can be cited as an example. The first exhaust portion 2302 ofthe first axial flow fan 2 and the second intake portion 3301 of thesecond axial flow fan 3 are connected to each other without any gap.With the above, air that has been discharged from the first exhaustportion 2302 of the first axial flow fan 2 can be prevented from leakingout through the connection between the first axial flow fan 2 and thesecond axial flow fan 3.

The first support ribs 24 are disposed on the exhaust side of the firstaxial flow fan 2. Furthermore, the second support ribs 34 are disposedon the intake side of the second axial flow fan 3. Furthermore, byconnecting the first axial flow fan and the second axial flow fan 3 toeach other in the axial direction, the surfaces of the first supportribs 24 facing the exhaust side and the surfaces of the second supportribs 34 facing the intake side overlap each other in the axialdirection. Note that the surfaces of the first support ribs 24 that facethe exhaust side and the surfaces of the second support ribs 34 thatface the intake side may be in contact with each other, or gaps may beformed therebetween to the extent that turbulent flow is not created. Inother words, the first support ribs 24 are disposed on the exhaust sideof the first housing 23, the second support ribs 34 are disposed on theintake side of the second housing 33, and the surfaces of the firstsupport ribs 24 that face the exhaust side and the surfaces of thesecond support ribs that face the intake side overlap each other in theaxial direction. With the above configuration, the first support ribs 24and the second support ribs 34 in combination form the stator blades.With the above, the velocity component of the airflow in the rotationdirection can be oriented towards the axial direction, and the pressureand the flow rate in the axial direction can be increased.

When the first axial flow fan 2 and the second axial flow fan 3 areconnected to each other, the inner flat surfaces 2341 of the secondinside diameter portion 234 of the first cylindrical portion 230 and theinner flat surfaces 3341 of the second inside diameter portion 334 ofthe second cylindrical portion 330 are disposed on the same plane.Furthermore, the inner curved surfaces 2342 of the second insidediameter portion 234 of the first cylindrical portion 230 and the innercurved surfaces 3342 of the second inside diameter portion 334 of thesecond cylindrical portion 330 are disposed on the same circularcylindrical surface. With such a connection, the second inside diameterportion 234 of the first cylindrical portion 230 and the second insidediameter portion 334 of the second cylindrical portion 330 are connectedto each other in the axial direction in a smooth manner.

In other words, the first housing 23 includes, at the end portion on theexhaust side, the square first exhaust flange portion 2321 that hassides that are each larger than the inside diameter of the inner surfaceof the first cylindrical portion 230. Furthermore, the second housing 33includes, at the end portion on the intake side, the square secondintake flange portion 3311 that has sides that are each larger than theinside diameter of the inner surface of the second cylindrical portion330. The first exhaust flange portion 2321 and the second intake flangeportion 3311 are connected to each other in the axial direction so as tooverlap each other, and the inside diameter D12 of the end portion ofthe inner surface of the first cylindrical portion 230 on the exhaustside that overlaps the corner portions of the first exhaust flangeportion 2321 in the radial direction, and the inside diameter D22 of theend portion of the inner surface of the second cylindrical portion 330on the intake side that overlaps the corner portions of the secondintake flange portion 3311 in the radial direction are larger than theminimum inside diameters D11 and D21, respectively, of the cylindricalportions 230 and 330, respectively, in the axial direction. By wideningthe connection between the first housing 23 and the second housing 33outwards with respect to the first inside diameter portion 233 and thefirst inside diameter portion 333, the flow velocity of the airflow inthe cylindrical portion is decreased. With the above, wind noisegenerated when the airflow passes the first support ribs 24 and thesecond support ribs 34 can be reduced. With the above, noise and (or)vibration can be suppressed. In other words, noise of the serial axialflow fan 1 can be reduced.

In the serial axial flow fan 1, the first axial flow fan 2 and thesecond axial flow fan 3 are driven at the same time. With the above, inthe serial axial flow fan 1, air is drawn in through the first intakeportion 2301 with the rotation of the first impeller 21. Furthermore,the first impeller 21 compresses and accelerates the air and dischargesthe air through the first exhaust portion 2302. The air that has beendischarged through the first exhaust portion 2302 of the first axialflow fan 2, while being prevented from leaking to the outside, flowsinto the second axial flow fan 3 through the second intake portion 3301.In the second axial flow fan 3, the air that has flowed in is compressedand accelerated further with the rotation of the second impeller 31, andis discharged from the second exhaust portion 3302. In other words, inthe serial axial flow fan 1, air is drawn in through the first intakeportion 2301 at the end portion of the first axial flow fan 2 on theupper side IS, is compressed and accelerated with the first impeller 21and the second impeller 31, and is discharged through the second exhaustportion 3302 at the end portion of the second axial flow fan 3 on thelower side. The second inside diameter portion 234 of the firstcylindrical portion 230 and the second inside diameter portion 334 ofthe second cylindrical portion 330 are connected to each other in theaxial direction in a smooth manner so that turbulence in the airflow issmall and decreases in air volume and pressure can be suppressed. In thewind tunnel of the serial axial flow fan 1 formed by connecting thefirst cylindrical portion 230 and the second cylindrical portion 330 toeach other, the inside diameter of the portion where the first axialflow fan 2 and the second axial flow fan 3 are connected to each other,in other words, the center portion in the axial direction, increases.With the above, the flow velocity of the airflow discharged through thefirst exhaust portion 2302 of the first axial flow fan 2 is decreased.With the above, the wind noise generated when the wind passes the firstsupport ribs 24 disposed at the lower end portion of the firstcylindrical portion 230, and the second support ribs 34 disposed on theintake side of the second housing 33 can be made smaller. By disposingthe surfaces of the first support ribs 24 that face the exhaust side andthe surfaces of the second support ribs 34 that face the intake sideoverlap each other in the axial direction, the first support ribs 24 andthe second support ribs 34 constitute the stator blades. The lower sidesOS of the first support ribs and the second support ribs 34 in the axialdirection are inclined surfaces that are oriented towards the downstreamside in the rotation direction of the first impeller 21. The airflowgenerated with the rotation of the first impeller 21 includes a velocitycomponent that swirls in the rotation direction of the first impeller 21and a velocity component in the axial direction. Furthermore, thevelocity component of the airflow in the circumferential direction isbent in the axial direction with the stator blades formed by the firstsupport ribs 24 and the second support ribs 34. With the above, thepressure and the flow velocity in the axial direction can be increased.Furthermore, by providing a gap between the first support ribs 24 andthe second support ribs 34, direct transmission of the vibration of thearmature 2223 and the vibration of the armature 3223 to each other canbe suppressed, and large vibration and (or) noise generated byinterference between the vibrations can be suppressed from occurring. Inother words, noise of the serial axial flow fan 1 can be reduced.

The first axial flow fan 2 includes auxiliary blade portions 213 in theouter edges of the first blades 211 of the first impeller 21 in theradial direction, and increases the pressure of the airflow dischargedthrough the first exhaust portion 2302. Airflow with high pressure isdischarged from the first axial flow fan 2. Furthermore, the airflowwith a high pressure discharged through the first exhaust portion 2302of the first axial flow fan 2 flows into the second axial flow fan 3through the second intake portion 3301.

Meanwhile, the second axial flow fan 3 has a larger number of bladescompared with the number of the first blades 211 of the first impeller21, and the inclination of the blades of the second axial flow fan 3with respect to the shaft is smaller than the inclination of the firstblades 211. Accordingly, the effect of increasing the flow rate of theairflow is larger in the second axial flow fan 3 than that in the firstaxial flow fan 2. The airflow from the first axial flow fan 2 having ahigh pressure is accelerated in the second axial flow fan 3 to increasethe flow rate. With the above, the serial axial flow fan 1 is capable ofdischarging an airflow having a high pressure and a large low rate. Asdescribed above, by providing the auxiliary blade portions 213 in theouter edge portions of the first blades 211 of the first impeller 21 inthe radial direction, the first axial flow fan 2 increases the pressureof the airflow generated by the first impeller 21. The first axial flowfan 2 has a high pressure increasing effect. The second axial flow fan 3has a high flow velocity increasing effect, in other words, a high flowrate increasing effect.

Features of the serial axial flow fan 1 according to the presentdisclosure were evaluated through computer simulations. Simulations wereconducted by changing Nin, Nout, and Nrib of the serial axial flow fan1, where Nin is the number of blades of the impeller of the axial flowfan on the intake side, Nout is the number of blades of the impeller ofthe axial flow fan on the exhaust side, and Nrib is the number of firstsupport ribs and the number of second support ribs. Note that in theconfiguration assuming the present disclosure, auxiliary blade portionsin which the outer sides thereof are warped towards the intake side wereformed in the outer edge portions of the blades of the impeller of theaxial flow fan in the radial direction.

A maximum efficiency point, the discharge pressure, and the flow rate ofan example of the conventional art including no auxiliary blades weremeasured, in a case in which Nin=5, Nout=7, and Nrib=11. Furthermore,measurements that are the same as those of the example of theconventional art were measured in a configuration, serving as theexemplary embodiment, satisfying Nin=5, Nout=7, and N=11 and includingauxiliary blade portions in the outer edge portions of the blades on theintake side in the radial direction.

As a result, while the maximum efficiency point of the example of theconventional art was 46%, that of the exemplary embodiment was increasedto 47%. Furthermore, regarding the pressure in a case in which the flowrate of the discharged airflow was 4.0 m³/min, while the example of theconventional art was about 1230 Pa, the exemplary embodiment was about1250 Pa. In the above case, while the input shaft power of the exampleof the conventional art was 168 W, that of the exemplary embodiment was165 W.

The maximum efficiency point of the exemplary embodiment was higher thanthat of the example of the conventional art, as well as the pressureunder the same flow rate. Furthermore, although the pressure-flowcharacteristics of the exemplary embodiment was higher than that of theexample of the conventional art, the input shaft power was lower.

As a result of the simulation, it was understood that in theconfiguration satisfying Nin<Nout<Nrib, when the auxiliary bladeportions were provided in at least either of the blades on the intakeside and the blades on the exhaust side, there were cases in which theefficiency was higher, the pressure was higher, and the air volume waslarger than a case in which there was no auxiliary blade.

Note that Nin, Nout, and Nrib are a set of prime integers. In otherwords, Nin, Nout, and Nrib are a set of integral numbers that do nothave a common divisor other than 1. With such a configuration,vibrational resonance between the first impeller 21, the second impeller31, the first support ribs 24, and the second support ribs 34 issuppressed. Noise caused by resonance is suppressed and the noise of theserial axial flow fan 1 can be reduced.

Furthermore, while changing Nin, Nout, and Nrib, similar simulationswere as carried out with a configuration satisfying Nin<Nout<Nrib, inwhich auxiliary blade portions were provided at the blades on the intakeside. A case satisfying (Nin, Nout, Nrib)=(5, 7, 11) was assumed as theexemplary embodiment, (Nin, Nout, Nrib)=(4, 7, 11) as a firstcomparative example, (Nin, Nout, Nrib)=(5, 9, 11) as a secondcomparative example, (Nin, Nout, Nrib)=(5, 11, 11) as a thirdcomparative example, and (Nin, Nout, Nrib)=(5, 7, 13) as a fourthcomparative example.

Furthermore, when the flow rate of the discharged air was 4.0 m³/min,the pressure in the first comparative example was about 800 kPa, thepressure in the second comparative example was about 990 kPa, thepressure in the third comparative example was about 1150 kPa, and thepressure in the fourth comparative example was about 990 kPa in the.

The number Nin of the blades of the impeller of the axial flow fan onthe intake side was five in the exemplary embodiment and was four in thefirst comparative example. It was understood that a pressure differenceis created in the discharged air depending on the number Nin of theblades of the impeller of the axial flow fan on the intake side.

The number Nout of the blades of the impeller of the axial flow fan onthe exhaust side was seven in the exemplary embodiment and was nine inthe third comparative example. It was understood that a pressuredifference is also created in the discharged air depending on the numberNout of the blades of the impeller of the axial flow fan on the exhaustside. The pressure of the discharged air was larger in the case ofNout=11 than in the case of Nout=9. Moreover, it was understood that inthe case of Nout=7, the pressure of the discharged air was even morelarger.

Moreover, the number Nrib of the first support ribs and the number Nribof the second support ribs in the exemplary embodiment were 11, andthose in the fourth comparative example were 13. It was understood thata pressure difference is created in the discharged air depending on thenumber Nrib of the first support ribs and that of the second supportribs. The pressure of the discharged air was larger in the case ofNrib=11 than in the case of Nrib=13.

In other words, the pressure-flow characteristics of the dischargedairflow in the exemplary embodiment was higher compared with the firstto fourth comparative examples.

Furthermore, as a result of conducting more simulations, it wasconfirmed that a configuration in which the auxiliary blade portionswere provided in the blades and in which Nin=5 was satisfied was mostoptimum in increasing the airflow. Furthermore, by satisfying Nout=7, itwas possible to increase the inclination and maintain the blade areas ofeach blades, and it was confirmed that Nout=7 is most optimum inincreasing the air volume. Furthermore, by satisfying Nrib=11, it wasconfirmed that the largest pressure and the largest wind force could beobtained while obtaining the required mechanical strength to support thefirst motor portion and the second motor portion in a stable manner atthe maximum efficiency point.

In the exemplary embodiment, the first impeller 21 and the secondimpeller 31 rotate in the same direction. Accordingly, by having thevelocity component of the airflow discharged in the circumferentialdirection from the first axial flow fan 2 and the rotation direction ofthe second impeller 31 be the same, the speed of the airflow in therotation direction relative to the speed of the end portions of thesecond blades 311 of the second impeller 31 on the upstream side becomessmall; accordingly, the vibration and noise can be suppressed. In otherwords, noise of the serial axial flow fan 1 can be reduced. Furthermore,since the above direction is the same as the direction of the airflowflowing into the second blades 311, resistance of the second blades 311can be suppressed. With the above, the input shaft power can besuppressed.

Note that the second blades 311 of the second impeller may be inclinedto opposite directions, and the rotation direction of the secondimpeller 31 may be opposite to the rotation direction of the firstimpeller 21. With the above, the effect of the second blades 311 of thesecond impeller 31 bending the velocity component of the airflow in therotation direction in the axial direction becomes larger. With theabove, the pressure of the airflow discharged from the serial axial flowfan 1 can be increased.

Furthermore, while the present embodiment includes the first axial flowfan 2 in which the auxiliary blade portions 213 are provided at theouter edge portions of the first blades 211 in the radial direction, theconfiguration is not limited to the above. The auxiliary blade portionsmay be provided at the outer edge portions of the second blades 311 inthe radial direction, which are provided in the second axial flow fan 3.Furthermore, the auxiliary blade portions may be provided at both of theouter edge portions of the first blades and the second blades in theradial direction. In other words, at least either of the first blades211 and the second blades 311 are provided with the auxiliary bladeportions 213.

Important capacities of the axial flow fan include pressure and airvolume. The serial axial flow fan 1 of the present disclosure can,overall, obtain a high pressure and a large air volume at the time ofmaximum efficiency by separating the two impellers 21 and 31 into animpeller for pressure (the first impeller 21) and an impeller for airvolume (the second impeller 31). In other words, by adding the auxiliaryblades (the auxiliary blade portions 213) to the impeller (the firstimpeller 21), a high pressure can be obtained and the impeller can beused as an impeller for pressure. The impeller for pressure (the firstimpeller 21) has a large pressure difference in each pressure surfaceand the corresponding negative pressure surface. Accordingly, air leaksthrough the gap between the outer peripheral portion of the impeller(the first blades 211), and the housing inner circumferential surface(the inner circumferential surface of the first cylindrical portion230), and pressure loss becomes large. The pressure loss can be reducedby providing the auxiliary blades (the auxiliary blade portions 213) atthe outer peripheral portion of the impeller (the first impeller 21).Meanwhile, by not providing any auxiliary blades in the impeller (thesecond impeller 31), the impeller can be used as an impeller for airvolume having a large air volume. The impeller for air volume (thesecond impeller 31) pushes the air with the entire surface to obtain alarge air volume. As described above, by combining the impeller forpressure (the first impeller 21) and the impeller for air volume (thesecond impeller 31), an airflow with high pressure and a large airvolume can be obtained.

While the exemplary embodiment of the present disclosure has beendescribed above, the exemplary embodiment can be modified in variousways within the scope of the present disclosure. The serial axial flowfan according to the present disclosure may be, for example, used as acooling fan that sends air to electronic components disposed insidedevices, such as a computer, a network communication device, and aserver, and cool the electronic components.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A serial axial flow fan comprising: a first axialflow fan that blows out air drawn in from an intake side to an exhaustside; a second axial flow fan connected to the first axial flow fanalong a central axis of the first axial flow fan, the second axial flowfan blowing out the air drawn in from an intake side to an exhaust side,wherein an end portion of the first axial flow fan on the exhaust sideand an end portion of the second axial flow fan on the intake side areconnected to each other; the first axial flow fan including a firstimpeller that rotates about the central axis, a first motor portion thatrotates the first impeller, a first housing that includes a firstcylindrical portion that surrounds an outside of the first impeller in aradial direction, and a first support rib that extends inwards from aninner surface of the first cylindrical portion and that supports thefirst motor portion; the first impeller including a plurality of firstblades that extend outwards in the radial direction and that arearranged in a circumferential direction; the second axial flow fanincluding a second impeller that rotates about the central axis, asecond motor portion that rotates the second impeller, a second housingthat includes a second cylindrical portion that surrounds an outside ofthe second impeller in the radial direction, and a second support ribthat extends inwards from an inner surface of the second cylindricalportion and that supports the second motor portion, a number of thesecond support ribs being equal to a number of the first support ribs;and the second impeller including a plurality of second blades thatextend outwards in the radial direction and that are arranged in thecircumferential direction; auxiliary blade portions being included in atleast either of the first blades and the second blades; andNin<Nout<Nrib being satisfied, where a number of first blades is Nin, anumber of second blades is Nout, and a number of first support ribs anda number of second support ribs are each Nrib.
 2. The serial axial flowfan according to claim 1, wherein the auxiliary blade portions areprovided at outer edge portions of the first blades in the radialdirection.
 3. The serial axial flow fan according to claim 2, whereinoutsides of the auxiliary blade portions in the radial direction arewarped towards the intake side.
 4. The serial axial flow fan accordingto claim 1, wherein Nin, Nout, and Nrib are a set of positive integersthat do not have a common divisor other than
 1. 5. The serial axial flowfan according to claim 1, wherein Nin is
 5. 6. The serial axial flow fanaccording to claim 1, wherein Nout is
 7. 7. The serial axial flow fanaccording to claim 1, wherein the first support rib is disposed on theexhaust side of the first housing, wherein the second support rib isdisposed on the intake side of the second housing, and wherein a surfaceof the first support rib that faces the exhaust side and a surface ofthe second support rib that faces the intake side overlap each other inan axial direction.
 8. The serial axial flow fan according to claim 1,wherein Nrib is 11.